In mixed signal Integrated Circuits (ICs), or particularly in System on Chip (SOC) circuits, several blocks are integrated in a single chip. Mixed-signal ICs are chips that include both digital and analog circuits on the same chip. For example, a single chip may be designed with different radio subsystems, including Global Positioning Systems (GPSs), Bluetooth systems, Wireless Local Area Network (WLAN) systems, and Frequency Modulation (FM) radio systems.
In such ICs, spurs caused by digital switching in underlying circuits may create co-existence issues among the blocks designed in the ICs. For example, switching transients in digital Metal Oxide Semiconductor (MOS) circuits perturb analog circuits integrated on the same die by means of coupling through the substrate. If the spurs due to digital switching in an aggressor block lie in the band of interest of a victim block, it may degrade performance of a radio circuitry of the victim block, As a possible solution, finding a unique frequency which is friendly to all radio circuitries in the ICs, is difficult.